The present invention relates to a glass-ceramic substrate for mounting LSI devices densely, particularly a glass-ceramic substrate which can be baked at low temperature, and a method of producing the same.
In parallel with the development of semiconductor technologies, there is an increasing demand for electronic apparatuses with miniature system configurations and operable at high speed. Today, semiconductor devices with high density and high integration are available in the form of VLSIs (Very Large Scale Integrated Circuits) and ULSIs (Ultra Large Scale Integrated Circuits). Mounting technologies for assembling VLSIs and ULSIs need extremely high density and fineness. Particularly, the prerequisite with a substrate for mounting semiconductor devices is that the wiring be fine enough to meet the increasing wiring density. Another prerequisite with this kind of substrate is that the dielectric constant of the material of the substrate be reduced, and dense wiring be enhanced in order to implement low wiring resistance and high-speed operation.
A glass-ceramic laminate substrate has been developed and put to practical use as an LSI substrate. Wiring conductors for use in this kind of substrate are implemented by Ag, Cu or similar low resistance metal. To produce a glass-ceramic laminate substrate, powder consisting of glass and ceramic is mixed with an organic binder so as to prepare a slurry. The slurry is dried to form a green sheet. After via holes have been formed in the green sheet, a conductive paste is buried in the via holes. Subsequently, a preselected electric circuit pattern is formed on the green sheet by screen printing. A plurality of green sheets each having such a structure are laminated and then baked at a temperature ranging from about 850.degree. C. to 1,000.degree. C.
However, at the temperature as high as 850.degree. C. to 1,000.degree. C., oxidation reduction occurs between Ag, Cu or a similar metallic conductor and the glass-ceramic, resulting in the interchange of electrons. In this condition, a potential difference occurs between two independent electric circuits which are not connected together. Consequently, Ag ions or Cu ions migrate through the glass along the electric field, and short the two independent circuits in due course of time. That is, while the two electric circuits are open before baking, they are shorted or the insulating resistance noticeably falls after baking. This kind of defect becomes more conspicuous with an increase in wiring density.